The present invention relates to cathode-grid assemblies for linear beam microwave vacuum tube devices having an electron emitting cathode and a microwave modulated grid closely spaced therefrom, and more particularly, to such an assembly including a support structure for the grid, wherein the support structure accommodates differential thermal expansion of a cathode assembly and the grid while maintaining an optimum grid-to-cathode spacing.
It is well known in the art to utilize a linear beam microwave vacuum tube device, such as a klystron or traveling wave tube amplifier, to generate or amplify high frequency, microwave RE energy. Such devices generally include an electron emitting cathode, an anode spaced therefrom, and a grid positioned in an inter-electrode region between the cathode and the anode. Grid to cathode spacing is directly related to the performance and longevity of the linear beam device. A problem that has long existed in the art is that during initial heat up, the grid to cathode spacing changes as the cathode is heated, thereby causing performance and reliability problems.
Prior solutions to this problem suggested a grid support structure that is closely connected to the cathode button. These solutions however required complicated mechanical means to deal with the different radial thermal expansion of cathode and grid. In order to electrically insulate the cathode and the grid a plurality of ceramic members was needed to connect the grid to the cathode button. These ceramic members create a plurality of difficulties because the ceramic members are mechanically stressed from the expansion difference. Thus, it would be very desirable to provide a cathode support structure for a linear beam device that maintains a proper spacing between the cathode and grid across the operating temperature range of the device. It would be further desirable to provide such a grid support structure which is formed of a one-piece ceramic. Further, some cases are known where the cathode support cylinder has changed its shape over time due to thermal stress by many heat cycles. In a grided tube with a grid support independent from the cathode button this would cause the cathode to short out with the grid or at least change the initial cathode grid spacing. In both cases the tube will fail early.
In accordance with one aspect a grid support structure maintains a proper grid-to-cathode spacing across an operating temperature range of the linear beam device.
Another aspect of the present invention also provides a cathode grid connection that allows the grid to follow all cathode movements.
In one aspect of the present invention a linear beam device has an axially centered cathode and an anode spaced therefrom. The anode and cathode are operable to form and accelerate an electron beam. The linear beam device includes an axially centered grid positioned between the cathode and the anode. The grid is operable to accept a high frequency control signal to density modulate the electron beam. A grid support is in contact with the cathode and the grid and keeps the spacing between the cathode and the grid constant, while electrically insulating them.
It is another aspect of the present invention to provide a linear beam device having a cathode and an anode. A linear beam device includes a grid positioned at a predetermined distance from the cathode between the cathode and the anode. The grid is operable to accept a high frequency control signal to density modulate a beam. A grid support supporting the grid which is operable to maintain the predetermined distance between the cathode and the grid throughout the operating temperature range of the linear beam device.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.